Abstract
BackgroundPlants are subjected to continuous stimuli from the environment and have evolved an ability to respond through various growth and development processes. Phototropism and gravitropism responses enable the plant to reorient with regard to light and gravity.ResultsWe quantified the speed of maritime pine seedlings to reorient with regard to light and gravity over 22 days. Seedlings were inclined at 15, 30 and 45 degrees with vertical plants as controls. A lateral light source illuminated the plants and stem movement over time was recorded. Depending on the initial angle of stem lean, the apical response to the lateral light source differed. In control and 15° inclined plants, the apex turned directly towards the light source after only 2 h. In plants inclined at 30° and 45°, the apex first reoriented in the vertical plane after 2 h, then turned towards the light source after 24 h. Two-dimensional gel electrophoresis coupled with mass spectrometry was then used to describe the molecular response of stem bending involved in photo- and gravi-tropism after 22 hr and 8 days of treatment. A total of 486 spots were quantitatively analyzed using image analysis software. Significant changes were determined in the protein accumulation of 68 protein spots. Early response gravitropic associated proteins were identified, which are known to function in energy related and primary metabolism. A group of thirty eight proteins were found to be involved in primary metabolism and energy related metabolic pathways. Degradation of Rubisco was implicated in some protein shifts.ConclusionsOur study demonstrates a rapid gravitropic response in apices of maritime pine seedlings inclined >30°. Little or no response was observed at the stem bases of the same plants. The primary gravitropic response is concomitant with a modification of the proteome, consisting of an over accumulation of energy and metabolism associated proteins, which may allow the stem to reorient rapidly after bending.
Highlights
Plants are subjected to continuous stimuli from the environment and have evolved an ability to respond through various growth and development processes
The same results were found by Fukaki et al [6], who repeated the experiment on Arabidopsis thaliana
In plants inclined at 30° (Figure 2C) and 45° (Figure 2D), the apex first reoriented in the vertical plane, before turning towards the lateral light source after 24 h
Summary
Plants are subjected to continuous stimuli from the environment and have evolved an ability to respond through various growth and development processes. Due to the ubiquitous presence of gravity on earth, it has been difficult to separate the effect of both gravity and light on plant growth and to study their interaction with regard to stem directional growth. Shoots responded to microgravity (through vertical growth) but in each experiment, lighting was vertical, the directions of gravity and light stimuli were parallel. Experiments in normal gravity where light exposure was unilateral have shown that the elongating apex grows towards the light [2,3]. This bending movement occurs due to changes in auxin gradients
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